Book/Report

FZJ-2020-00424

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Die $\alpha$2-Untereinheit zyklisch Nukleotid-gesteuerter Ionenkanäle von Säugetieren: Lokalisation in Retina und Riechepithel und elektrophysiologische Charakterisierung

Angele, A. (Corresponding author)FZJ*

2000
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/23971

Report No.: Juel-3771

Abstract: In the first part of this PhD-thesis heterologously expressed bCNC$\alpha$2- und bCNC$\alpha$2/$\beta$la-channels and native CNG-channels in bovine cone outer segments were characterized electrophysioloogically. In particular, channel block by $\textit{l-cis}$ Diltiazem, relative permeability for]Li$^{+}$ and the possibility to modulate the channels with Calmodulin (Ca$^{2}$/CaM) were examined. These experiments should clarify if the channels in cone outer segments are bCNC$\alpha$-2-homomeric or heteromeric channels. Comparison of the results clearly demonstrate that CNG-channels of cone outer segments are not bCNC$\alpha$2-homomers. Relative permeability of Li$^{+}$ and immunocytochemical stainings suggest that bCNC$\beta$la is not themodulatory subunit of these channels. In the second part it was demonstrated by immunocytochemistry that rCNC$\alpha$2-subunits are expressed in cone outer segments of the retina and in a subpopulation of olfactory neurons. These olfactory neurons coexpress PDE2 (a cGMP-depend isoform of phosphodiesterase) and GC-D (a receptor guanylyl cyclase). The expression of the main components of the cAMp-dependent signal transduction cascade of prototypic olfactory neurons (G$_{olf}$, ACIII and the CNG-channel subunits rCNC$\alpha$3 and rCNC$\beta$lb) cannot be demonstrated by immunoc<tochemistry in this subpopulation. Hence, PDE2/GC-D/$\alpha$2-cells use an alternative cGMP-dependent signal transduction pathway including rCNC$\alpha$2-channels as target. Heterologously expressed rCNC$\alpha$2-channels are cGMP-gated unselective cation channels. Homomeric channels formed by the splice variants rCNC$\alpha$2 or rCNC$\alpha$2b do not differ significantly with respect to ligand selectivity, ligand affinity and modulation by Ca$^{2+}$/CaM. They are highly selective for cGMP with K$_{½}$-values of 3 $\mu$M for cGMP und 300 - 600 $\mu$M for cAMP, respectively, but can be activated by saturating cGMP and cAMP concentrations to the same extent. Homometric rCNC$\alpha$2/$\beta$1b- and rCNC$\alpha$2/$\alpha$4-channels are slightly less sensitive for cGMP than the homomeric rCNC$\alpha$2-channels with K$_{½}$-values of about 10 $\mu$M for both the heteromeric channels. Nevertheless, these heteromeric channels are still highly selective for cGMP. In rCNC$\alpha$2/$\beta$1b-heteromeric channels the ratio I$_{cAMP}$/I$_{cGMP}$ for saturating ligand concentration is 1, in rCNC$\alpha$2/$\alpha$4-channels about 0.7. In both rCNC$\alpha$2-homomeric and rCNC$\alpha$2/$\beta$1b-heteromeric channels a halfmaximal cGMP-induced current is reduced by Ca$^{2+}$/CaM by 50%. The kinetics of this effect can be descibed with second order exponential functions and are slightly faster in the heteromeric channels.

---

Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000 ; Retrocat)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

---

Database coverage:

---